usbstring.c revision 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 
1/*
2 * Copyright (C) 2003 David Brownell
3 *
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU Lesser General Public License as published
6 * by the Free Software Foundation; either version 2.1 of the License, or
7 * (at your option) any later version.
8 */
9
10#include <linux/errno.h>
11#include <linux/kernel.h>
12#include <linux/list.h>
13#include <linux/string.h>
14#include <linux/device.h>
15#include <linux/init.h>
16
17#include <linux/usb_ch9.h>
18#include <linux/usb_gadget.h>
19
20#include <asm/unaligned.h>
21
22
23static int utf8_to_utf16le(const char *s, __le16 *cp, unsigned len)
24{
25	int	count = 0;
26	u8	c;
27	u16	uchar;
28
29	/* this insists on correct encodings, though not minimal ones.
30	 * BUT it currently rejects legit 4-byte UTF-8 code points,
31	 * which need surrogate pairs.  (Unicode 3.1 can use them.)
32	 */
33	while (len != 0 && (c = (u8) *s++) != 0) {
34		if (unlikely(c & 0x80)) {
35			// 2-byte sequence:
36			// 00000yyyyyxxxxxx = 110yyyyy 10xxxxxx
37			if ((c & 0xe0) == 0xc0) {
38				uchar = (c & 0x1f) << 6;
39
40				c = (u8) *s++;
41				if ((c & 0xc0) != 0xc0)
42					goto fail;
43				c &= 0x3f;
44				uchar |= c;
45
46			// 3-byte sequence (most CJKV characters):
47			// zzzzyyyyyyxxxxxx = 1110zzzz 10yyyyyy 10xxxxxx
48			} else if ((c & 0xf0) == 0xe0) {
49				uchar = (c & 0x0f) << 12;
50
51				c = (u8) *s++;
52				if ((c & 0xc0) != 0xc0)
53					goto fail;
54				c &= 0x3f;
55				uchar |= c << 6;
56
57				c = (u8) *s++;
58				if ((c & 0xc0) != 0xc0)
59					goto fail;
60				c &= 0x3f;
61				uchar |= c;
62
63				/* no bogus surrogates */
64				if (0xd800 <= uchar && uchar <= 0xdfff)
65					goto fail;
66
67			// 4-byte sequence (surrogate pairs, currently rare):
68			// 11101110wwwwzzzzyy + 110111yyyyxxxxxx
69			//     = 11110uuu 10uuzzzz 10yyyyyy 10xxxxxx
70			// (uuuuu = wwww + 1)
71			// FIXME accept the surrogate code points (only)
72
73			} else
74				goto fail;
75		} else
76			uchar = c;
77		put_unaligned (cpu_to_le16 (uchar), cp++);
78		count++;
79		len--;
80	}
81	return count;
82fail:
83	return -1;
84}
85
86
87/**
88 * usb_gadget_get_string - fill out a string descriptor
89 * @table: of c strings encoded using UTF-8
90 * @id: string id, from low byte of wValue in get string descriptor
91 * @buf: at least 256 bytes
92 *
93 * Finds the UTF-8 string matching the ID, and converts it into a
94 * string descriptor in utf16-le.
95 * Returns length of descriptor (always even) or negative errno
96 *
97 * If your driver needs stings in multiple languages, you'll probably
98 * "switch (wIndex) { ... }"  in your ep0 string descriptor logic,
99 * using this routine after choosing which set of UTF-8 strings to use.
100 * Note that US-ASCII is a strict subset of UTF-8; any string bytes with
101 * the eighth bit set will be multibyte UTF-8 characters, not ISO-8859/1
102 * characters (which are also widely used in C strings).
103 */
104int
105usb_gadget_get_string (struct usb_gadget_strings *table, int id, u8 *buf)
106{
107	struct usb_string	*s;
108	int			len;
109
110	/* descriptor 0 has the language id */
111	if (id == 0) {
112		buf [0] = 4;
113		buf [1] = USB_DT_STRING;
114		buf [2] = (u8) table->language;
115		buf [3] = (u8) (table->language >> 8);
116		return 4;
117	}
118	for (s = table->strings; s && s->s; s++)
119		if (s->id == id)
120			break;
121
122	/* unrecognized: stall. */
123	if (!s || !s->s)
124		return -EINVAL;
125
126	/* string descriptors have length, tag, then UTF16-LE text */
127	len = min ((size_t) 126, strlen (s->s));
128	memset (buf + 2, 0, 2 * len);	/* zero all the bytes */
129	len = utf8_to_utf16le(s->s, (__le16 *)&buf[2], len);
130	if (len < 0)
131		return -EINVAL;
132	buf [0] = (len + 1) * 2;
133	buf [1] = USB_DT_STRING;
134	return buf [0];
135}
136
137